Pressor Response to Static and Dynamic Knee Extensions at Equivalent Workload in Humans

Abstract

Static exercise has been thought to induce greater pressor response than dynamic exercise, but in contrast it has been recently reported that repetitive muscle contraction recruiting small muscles evokes greater response than sustained contraction. It remained unknown whether sustained contraction induces greater pressor response if large muscles were recruited. Nine subjects performed three types of isometric knee extensions recruiting the large muscle group, i.e., 2-min sustained (20% and 40% maximal voluntary contraction [MVC]) and 4-min repetitive (40% MVC, duty cycle = 1:1 s) muscle contractions. Compared under the equivalent TTI and exercising duration (2 min), the changes in femoral arterial blood flow and VO₂ from baseline (ΔBF, ΔVO₂) were significantly less during sustained contraction than during repetitive contraction (sustained vs. repetitive; ΔBF: +92 ± 195 vs. +1,174 ± 269 ml min⁻¹, ΔVO₂: +53 ± 12 vs. +180 ± 32 ml min⁻¹, mean ± SE, p < 0.05), although the change in mean arterial pressure (ΔMAP) was greater during sustained contraction (+24 ± 3 vs. +19 ± 3 mmHg). Compared under the equivalent TTI and peak tension (40% MVC), ΔBF and ΔVO₂ were less and ΔMAP was greater during sustained contraction (ΔBF: −296 ± 176 vs. +868 ± 272 ml min⁻¹; ΔVO₂: +104 ± 16 vs. + 212 ± 46 ml min⁻¹; ΔMAP: +37 ± 8 vs. +20 ± 4 mmHg). Moreover ΔMAP during postexercise occlusion of the active limb was significantly greater after sustained contraction than after repetitive contraction (+17.0 ± 2.8 vs. +9.5 ± 4.4 mmHg). These results demonstrated that pressor response is greater during sustained than during repetitive contraction, recruiting a large muscle group. This finding should be mainly due to the greater accumulation of metabolites in active muscles during sustained contraction.